Surface acoustic wave induced thermal lysis of red blood cells in microfluidic channel

Xueyong Weia, Lang Nana, Juan Rena, Xiaolong Liub and Zhuangde Jianga

aState Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, China bThe Liver Center of Fujian Province, Fujian Medical University, Fuzhou 350025, P. R. China

ABSTRACT In this paper, we present a novel surface acoustic wave (SAW) method for continuous red

blood cell lysis. Assisted by the SAWs, 95% cell lysis was achieved in the microfluidic channel. Through changing the supplied electrical signal, the effects of different parameters on lysing efficiency were studied. To further explore the lysis mechanism, different factors induced by SAWs were analyzed. This method provides a new approach for continuous cell lysis, which can be potentially integrated with biochips for DNA extraction to realize the high efficiency cell pretreatment system. KEYWORDS: Cell lysis, Microfluidics, Surface acoustic wave, Thermal effect

INTRODUCTION

Cell lysis is a process to break up cell membrane to access intracellular components for further analysis [1]. Normally, it is achieved by some chemical [2] or physical [3] methods. However, both of these methods have some disadvantages [4]. Recently, with the active investigation of surface acoustic wave (SAW), its high energy density and non-contact forces provide good bases for the realization of a new lysis method.

Based on the acoustic streaming and radiation forces, SAWs have been applied to a series of cell manipulation researches, such as cell patterning, cell sorting, and so on [5]. Furthermore, utilizing a square phononic lattice, Reboud et al [6] actuated asymmetric SAWs acting on the blood sample, which can create vortices to achieve rapid blood cell concentration and lysis. Although having a high efficiency, this method can only be applied to droplet samples, which will bring difficulties for the extraction of required components and realization of continuous cell pretreatment. Here, we present a novel SAW method for continuous cell lysis in a PDMS channel, which has good potential to be integrated with subsequent extraction and amplification biochips for continuous cell analysis.

EXPERIMENTAL

The fabrication process of the SAW-based lysis chip consists of three steps including patterning of IDTs, fabrication of PDMS channel and bonding of the channel to the substrate. Specifically, the IDTs were patterned on a LiNbO3 wafer (Y+128° X, SIOM, CN) using a lift-off technique. Then the PDMS channel was fabricated using a soft lithography replica molding technique. Finally, after 40 s’ oxygen plasma treatment (PDC-32G, Harrick, USA), the PDMS channel and substrate with patterned IDT were aligned and heated at 150 for 3 h to complete bonding. The two sets of IDTs were designed to have 5 and 20 pairs of electrodes with uniform width of 250 μm, thus having a resonance frequency of 4 MHz. The width and depth of the channel were designed to be 400 μm and 64 μm, respectively.

To generate the SAWs acting in the PDMS channel, an AC signal generated by an arbitrary signal generator (AFG3022, Tektronix, USA) was amplified with a power amplifier (BA4850, NF, JP) and supplied to the IDT. The lysis process and morphological change of the cells were recorded by a microscope (LV100, Nikon, JP) and a CCD camera (DS-Fi1, Nikon, JP), as shown

2062978-0-9798064-8-3/µTAS 2015/$20©15CBMS-0001 19th International Conference on Miniaturized Systems for Chemistry and Life Sciences October 25-29, 2015, Gyeongju, KOREA

in Fig. 1. In addition, to investigate the relation between electrical signal and lysing efficiency, the start time and end time of the blood cell lysis were detected at different electrical signals.

Figure 1: Schematic illustration of the experimental setup.

Figure 2: (a) Lysis process of the red blood cells. (b) Morphological change of the single cell. Scale bars are (a) 50 μm and (b) 10 μm, respectively.

RESULTS AND DISCUSSION

Supply the 20-pair-electrode IDT with an electrical signal of 13.15 MHz and 1.6 W, which has a strong response, obvious blood cell lysis was observed in the PDMS channel, as shown in Fig. 2 (a). The blood cells were initially focused into several lines under the action of acoustic radiation forces. Then after about 20 s, lysis occurred in the center and spread to the ends. Finally, the whole complete lysis was achieved after about 45 s. Through counting the intact cells at different locations, it was found that over 95% blood cells were lysed. As for the single cell, it gradually became transparent accompanied by the release of hemoglobin, and finally out of sight after about 2 s, as shown in Figure 2 (b).

Fig. 3 shows the effect of electrical signal on the lysing efficiency. The lysis time versus frequency curve (Fig. 3 a) indicates that the lysis only occurs at frequencies around 13.15 MHz, and the lysis time decreases as the frequency approaches the strongest point. And the lysis time versus power curve (Fig. 3b) shows that the lysis time initially decreases as the power increases, and then becomes stable after the power exceeds a threshold of 2.8 W, which can be considered as the minimum value for efficient blood cell lysis. A similar variation trend (Fig. 3c) was also achieved at the IDT with added electrodes, despite the lysis time being significantly decreased, which can be as short as 30 s.

Figure 3: (a) Lysis time change for different frequencies (5-pair-electrode IDT). (b) Lysis time change for different powers (5-pair-electrode IDT). (c) Lysis time change for different powers (20-pair-electrode IDT).

To further explore the lysis mechanism, the potential factors were concluded as acoustic

radiation force, shear stress, and thermal effect. Through calculations and simulations, the acoustic

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radiation force is in the order of 10-12 N, which is not enough to induce cell deformation, and the shear stress, maximum to 23 Pa, is also below the threshold for extensive blood damage. To evaluate the effect of thermal effect, the temperature rise of the PDMS channel was detected at different powers, as shown in Fig. 4. Combined with Fig. 3 (b), it can be found that the blood cell lysis will start as the temperature exceeds 85 C, which maybe the effective temperature for thermal lysis. Therefore, the cell lysis can be attributed to the SAW-induced temperature rise.

Figure 4: (a) Temperature variation of the PDMS channel for different powers (5-pair-electrode IDT). (b) Ultimate thermal distribution on the surface of the PDMS.

CONCLUSION

This paper presented a novel SAW-based lysis method, which can achieve 95% red blood cell lysis in the PDMS channel. Through changing the supplied electrical signal, the effects of different parameters on lysing efficiency were studied. Furthermore, after analyzing the potential factors, the lysis mechanism was intensively explored, which finally indicated that the thermal effect causes the occurring of cell lysis. Compared with previous works, this method can perform continuous cell lysis with a high lysing percentage, which has good potential to be integrated into the micro total analysis system (μTAS).

ACKNOWLEDGEMENTS This work is supported by the National Key Scientific Instrument and Equipment Development Program of China (No.2012YQ030261), 111 Project (No.B12016), the Fundamental Research Funds for the Central Universities xjj2015107 and the open fund from United Innovation of Mengchao Hepatobiliary Technology Key Laboratory of Fujian Province (2014ZDSY2001). REFERENCES [1] J. EL-Ali, P. K. Sorger, and K. F. Jensen, “Cells on chips,” Nature, 442, 403-411, 2006. [2] X. Chen, D. Cui, C. Liu, and H. Cai, “Microfluidic biochip for blood cell lysis,” Chin. J.

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